Context

Monitoring large industrial installations is a necessary step in order to ensure their security. However, this monitoring brings multiple issues. Generally, this task cannot be performed by a wired network, as the installations have not be designed for such a network; this is the case for water dams for example. The monitoring has to be done by a wireless network, but the presence of several metallic machinery greatly deteriorates radio communications. Most of the network protocols are not designed to environments with very bad propagation conditions.

The maintenance of the sensors is another problem. On the one hand, the location of the sensors cannot be chosen arbitrarily. It has to match an area that can be reached and that does not disrupt the installation operation. On the other hand, the maintenance of sensors has to occur rarely. Indeed, if we go back to the water dam example, it is easy to notice that changing batteries every month is not realistic.

Objectives and achievements

The OCARI project

OCARI stands for the Optimisation of Communications of Ad hoc Industrial Networks. The purpose of the project is to propose a mechanism that can be applied in an industrial environment to monitor industrial installations.

The task of our team in OCARI is to propose a deterministic and energy-efficient MAC protocol. Determinism allows the protocol to guarantee that generated traffic (periodic measurements or alarms) can circulate through the network in a bounded time, while reducing the loss probability due to interferences. The energy efficiency of the protocol reduces the frequency of battery changes.

The MaCARI protocol

MaCARI global cycle and its three periods.

The MACARI protocol is an outcome of the OCARI project. This protocol divides time into a global cycle constituted of three periods: a synchronisation period, a scheduled activities period and an unscheduled activities period. During the synchronization period, all the devices of the network are synchronized by the means of a beacon. The beacon is propagated according to an order specific by the network coordinator. During the scheduled activities period, the network is considered as a tree and a time slot is allocated for each set of devices to perform local or tree-based communications. Finally, the period of unscheduled activities allows the devices that are in range to communicate (without using necessarily the links of the tree).

MaCARI integrates features that allow end-to-end communications. Those communications can be seen as the way salmons swim up rivers (see the picture at the top of this web page). When they swim up a river, salmons might reach waterfalls. At this point, they have two options. The first option is to find a detour path, that takes longer but is guaranteed. The second option is to try to jump up the waterfall. Similarly, the devices have two options to communicate: they can use the tree as a guaranteed communication path, but that solution leads to long delays. Alternatively, devices can try to communicate directly with the devices in range, but in this case they have to win the competition for the medium first.

Resources

The French national agency for research is funding the project, and the PhD thesis of Gérard Chalhoub, who is working on the MaCARI protocol (from its design to its implementation, including its validation and performance measurements). This work leads to the study of IEEE 802.15.4, and particulary the slotted CSMA/CA algorithm.